(1) Field of the Invention
The invention relates to a glass substrate cassette, and more particularly to a cassette for supporting large-size glass substrates.
(2) Description of the Related Art
With prosperous growth in Thin Film Transistor Liquid Crystal Display (TFT LCD) technology, the TFT LCD has gradually displaced the cathode ray tube (CRT) display in the market and become the mainstream of the display technology. The TFT LCD having various advantages such as compactness in size, low power consumption and low radiation is widely applied to electronic products such as personal digital assistants (PDAs), mobile phones, digital video cameras, digital cameras, notebook computers, and televisions.
One of key components in a typical TFT LCD is a glass substrate. The glass substrate has a large amount of thin film transistors formed thereon. These transistors serve as switch devices for controlling pixel brightness of the display, in which the pixel is the basic element in the TFT LCD for forming a desired image on the liquid crystal display. In manufacturing the TFT LCDs, a cassette is usually used to transport and/or buffer the fragile glass substrates.
Referring to FIG. 1A, a conventional cassette 1 for stacking a plurality of glass substrates 4 is illustrated. As shown, the cassette 1 is formed as a hollow container 10 with a fully-open transporting gate 11 in a front side. A plurality of pairing support pins 12 are affixed to opposing lateral sides of the transporting gate 11. A socket 13 is therefore formed between adjacent support pins 12. The glass substrates 4 can be stored into the respective sockets 13 and thus supported by the underneath support pins 12. In this design, a delivery device 5 can be used to load/unload the substrates 4 with respect to the sockets 13.
For the sixth-generation TFT LCDs, a conventional cassette 1 may store broad and thin glass substrates that have a dimension of about 1500 mm×1850 mm. When the glass substrate 4 is supported by the support pins 12 as shown in FIG. 1B, the substrate 4 will deflect downward to form a concave shape due to the gravity. It is apparent that an abrupt contact between the delivery device 5 and the brittle glass substrate 4 during the loading/unloading process may break the glass substrate 4 and cause irreversible damage to the substrate 4.
Referring to FIG. 2A, another conventional cassette 2 having a plurality of support wires 21 connecting two opposing lateral sides of the cassette 2 is shown. The socket 22 may be formed between every two adjacent support wires 21. The glass substrate 4 is stored in the socket 22 and supported by the support wires 21. However, the glass substrate 4 still deflects concavely due to its own weight and the flexibility of the support wire 21.
To overcome the problem of deflection of the substrate 4 in the cassette, transport rollers 6 can be introduced into the cassette 4 for bearing the glass substrates 4, as shown in FIG. 2B. The transport rollers 6 may approach the glass substrate 4 from the bottom of the cassette 2 to lift the glass substrate 4 and unload the glass substrate 4 from the cassette 2, as shown in FIG. 2B.
Generally, the substrates 4 are unloaded from the bottom of the cassette 2 to the top. On the other hand, the loading of the substrates 4 into the cassette 2 needs to follow a top-to-bottom order. It is clear that such design of the cassette 2 are unable to load/unload the substrates 4 in an arbitrary order.
Referring to FIG. 3, it shows a third conventional cassette 3. As compared to the above designs, the cassette 3 has parallel back support rods 33 affixed to the back side 32 of the cassette 3. The back support rod 33 is a cantilever extending toward the transporting gate 34 to support the glass substrate. However, the cantilever back support rod 33 also deflects and thus the problem associated with concave substrates in the cassette 3 still remains.
The disadvantages mentioned above are getting worse, especially when the glass substrate is broad and thin. In particular, with the brittle glass substrate stored in the cassette as described above, even a small impact or a low-energy vibration with a frequency close to the nature resonance frequency of the substrate may easily break the substrate.